This invention relates to valve stem seals utilized in intake and exhaust manifolds of internal combustion engines. More particularly, this invention relates to concentricity of valve stem sealing elements about valve stems.
Valve stem seals of the type including resilient seal bodies supported within rigid cylindrical casings or shells are available in many designs and configurations. Most designs address the efficiency of the actual sealing lip portions of such seals, primarily as related to the "metering" of oil flow between the interface of the lip and the stem.
Generally the rigid cylindrical shell is fixedly supported on a valve stem guide, with the inside diameter of the shell frictionally engaging the outside diameter of the guide. Although the shell supports a sealing element adapted to be centered about the valve stem, it will be apparent to those skilled in the art that as a practical matter the valve stem and valve guide are rarely concentrically positioned. Generally, this is not a serious problem where the support portion of the shell and the lip portion of the seal body are relatively far apart. However, as the latter spacing becomes smaller, there is less flexibility in the body of the seal to accommodate radial offset between stem and guide. When eccentricity is extreme, resultant distortion of the seal body can cause non-uniform pressures on the sealing element, which in turn produces undesirable wear patterns and unpredictable oil control.